1. Field of the Invention
The present invention relates to methods and apparatuses of recording and reproducing digital data stream on a recording medium such as a high-density digital versatile disk (called ‘HD-DVD’ hereinafter).
The present invention further relates to a recording medium on which digital data stream has been written.
2. Description of the Related Art
Owing to technical improvement in the fields of video/audio data compression, digital modulation/demodulation, and so on, a digital television broadcast system broadcasting IV signals in the form of digital data stream is being standardized rapidly.
In the digital television broadcast system, audio/video (A/V) signals to be broadcast are compressed according to the data compressing rule specified by MPEG 2 (Moving Picture Experts Group) and the compressed A/V data are broadcast in the form of a transport stream (TS), which is also defined in the MPEG 2 standard, composed of a series of 188-byte-long transport packets (TPs).
The digital TV broadcast system, which will be commercialized soon owing to technical improvement of A/V data compression and transmission, is able to support much higher-quality of video and audio than an analog TV system. Furthermore, it ensures data compatibility with a digital communication device, a digital storage device, etc.
In the meantime, a new device is being developed to prepare for commercialization of a digital TV broadcast system. That is a digital recorder able to receive a TS of digital broadcast programs and record it on a writable HD-DVD is being developed. Such a digital recorder will be widely used as the digital TV broadcast system is commercialized in earnest.
Digital A/V data compressed in the manner of MPEG 2 for the digital TV broadcast system are composed of I- (Intra-), P- (Predictive-), and B- (Bidirectionally predictive-) pictures. An I picture is a basic picture and a P or a B picture can be presented as a video frame if there is an associated I picture.
In the digital TV broadcast system, the compressed digital A/V data are divided and inserted in each payload field of a series of 188-byte-long (inclusive of header) TPs, which are broadcasted sequentially.
Then, the digital recorder would record the TPs carrying TV broadcast programs on a writable HD-DVD in the same order as they are received. During the recording operation, a predetermined-sized, e.g., 4-byte time stamp indicative of packet arrival time may be added to each TP.
If the recorded TPs reaches some pack amount, e.g., 32 packs during the TP recording, the digital recorder groups those packets into a single ‘high-density stream object unit’ (called ‘HOBU’ hereinafter) and creates and writes search information for that HOBU as navigation data. The search information includes location or location-associated time information pointing to the head of a HOBU.
However, if the broadcasted TPs are recorded in the same order as they are received as aforementioned, the head of each HOBU is not aligned with the start of an arbitrary picture as shown in FIG. 1. In case that digital data stream has been recorded as shown in FIG. 1, when the digital recorder searches the recorded digital data stream for a certain scene equivalent to a picture a user wants to view, it searches by jumping in the unit of HOBU with reference to the stored search information for all HOBUs.
However, because a HOBU includes the rest data of a previous picture in its head area as shown in FIG. 1, a complete video frame can not be constructed from the data in the head area. Therefore, the digital recorder must discard the remaining data of a previous picture in the current HOBU and obtain a complete picture data from successive TPs following the discarded data. After the obtained complete picture data are presented as a video frame, the digital recorder may confirm whether or not reproduction is to be started from the presented picture based on user's command, e.g., ‘continue searching’ or ‘play’.
However, the additional searching operation within a HOBU for a complete picture takes more searching time. Namely, it makes random accessibility of recorded digital data stream difficult.
If the remaining data of a previous picture are output without discarding, noise might be generated in a video frame.
Consequently, if a digital data stream of digital TV broadcast programs are recorded as they are received, the aforementioned disadvantages would arise inevitably.
On the other hand, if a read-only HD-DVD containing an A/V digital data stream to be presented through a digital television set is manufactured, without any consideration of alignment of the head of each HOBU with picture start, in the manner that digital data stream is divided and filled in each payload field of successive TPs with which HOBUs are packed, as illustrated in FIG. 1, then, such-manufactured read-only HD-DVD would still have the aforementioned drawbacks such as bad random-accessibility.